South Korea ( listen), officially the Republic of Korea (ROK;  listen), is a sovereign state in East Asia, constituting the southern part of the Korean Peninsula.[11] Officially, its territory consists of the whole Korean Peninsula and its adjacent islands,[12] which are largely mountainous. South Koreans lead a distinctive urban lifestyle, as half of them live in high-rises[13] concentrated in the Seoul Capital Area with 25 million residents.[14] The capital Seoul is the world's sixth leading global city[15] with the fifth largest economy[16] and is the seventh most sustainable city in the world.[17]